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Unit 3 Worksheet 4 – Quantitative Energy Problems
Energy constants (H2O)
4.18 J/g˚C = 1.00 cal/g˚C Heat capacity (c) of liquid water
2.1 J/g˚C = 0.50 cal/g˚C Heat capacity (c) of solid water
For each of the problems:
a) Sketch a warming or cooling curve to help you decide which heat capacity constant to use to solve the problem. Identify the system by drawing an energy flow diagram.
b) Solve the problem. Show your set-up with clearly labeled units throughout! Keep a reasonable number of sig figs in your answers.
1. A cup of coffee (140 g) cools from 75˚C down to comfortable room temperature 20.˚C. How much energy does it release to the surroundings?
2. Suppose that during the Icy Hot lab that 65 kJ of energy were transferred to 450. g of water at 20.˚C. What would have been the final temperature of the water?
3. How many grams of water can be heated from 20.0 C to 75.0 C using 837 joules?
4. The heat capacity of solid iron is 0.447 J/g˚C. If 304 kJ energy were transferred to a 450 g chunk of iron at 20.˚C, what would be the final temperature?
5. How much energy is needed to raise the temperature of 150. g of ice from –16.0 oC to –8.0 oC?
6. How much energy is transferred when 340. g of water cool from 75oC to 50.oC? Must energy be added to or removed from the system for this process to occur?
7. Most engine blocks are currently made from aluminum. In testing, a sample aluminum engine block is heated from room temperature (20. oC) up to 312 oC by absorbing 4.47 x 103 kJ of energy. What is the mass of the engine block? The heat capacity of solid aluminum s 0.897 J/goC.
Modeling Chemistry 1 U3 ws4 v2.0